What Was Wrong with the Boiler Pump?

We came home from vacation to no heat. The boiler was firing but the Grundflos secondary pump was not running to distribute it through the radiant pipes. The first thing I did was turn off the heat function of the boiler so it would not overheat the primary pump. I had changed the wiring for the pumps several times. I tried wiring both the primary and secondary pumps to come on separately, but I had pressure issues and I burned out the secondary Taco 011 pump so I wired them in series for the valve controller to turn them both on at once. When I replaced the Taco with the Grundflos pump they were wired separately again. The final wiring that seemed to work was to install an outlet that only came on when the valve controller called for heat. That separated the wiring for the pumps and connected the secondary pump to its own electrical box.

When I saw the pump was not displaying information and it did not respond to pressing buttons, I assumed it was burned out. I tested the outlet and saw there was power so I was set to order a replacement when I decided to plug it in another outlet. It came right on. So the pump was fine but the outlet was having a problem. One side was dead but the other was OK. I plugged the pump back in but the outlet gave a pop and blew the circuit. I was too tired to investigate further so we had no heat overnight. Luckily we are solar heated so our inside temperature stayed comfortable.

It was cloudy and cold the next day so the house was getting chilly. I let the pump run since the pipes were warm but the valve controller is connected to the blown circuit and I could not just disconnect the wiring to turn it back on. The boiler was not getting a call for heat from the non-functioning zone controller. So I opened the outlet box and looked for the problem.

Shorted ground wire in box
Shorted ground wire in box

It was obvious that the ground wire had shorted! There was too much ground wire in the box and it was a piece of old wire I had reused so the ground was not insulated. I solved the problem by cutting the ground shorter and not grounding it to the box. The shorter wire was pushed to the rear of the box. I’m not sure why the wiring was loose enough for the outlet to move and touch the wire. But it obviously happened especially when I blew the circuit by pushing on the outlet with the pump plug.

Once I got the wiring properly out of the way I reinstalled the outlet and reconnected it to the valve controller. The first time one of the white wires was loose on the valve controller and I was getting only 54 volts at the outlet. I switched off the breaker again and found the loose wire. Finally when I reconnected that wire and reset the circuit the power to the valve controller was restored. The boiler was getting a signal when there was a call for heat. I plugged in the Grundfos pump and everything worked again. We had the house nice and toasty in a couple of hours.

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